Add testing instructions and contributing links (#2)

* Add contributing and CoC

* Add CONTRIBUTING.md

* line length

* refer to remote contributing guide, borrow test instructions

* Un-artisinally craft contributing link

Author: jisantuc

README.md

@@ -48,3 +48,51 @@ The following types should be used as applicable `rel` types in the
 | Type                | Description |
 | ------------------- | ----------- |
 | fancy-rel-type      | This link points to a fancy resource. |
+
+## Contributing
+
+All contributions are subject to the
+[STAC Specification Code of Conduct](https://github.com/radiantearth/stac-spec/blob/master/CODE_OF_CONDUCT.md).
+For contributions, please follow the
+[STAC specification contributing guide](https://github.com/radiantearth/stac-spec/blob/master/CONTRIBUTING.md) Instructions
+for running tests are copied here for convenience.
+
+### Running tests
+
+The same check-markdown and check-examples programs that runs as a check on PR's is part of the repo and can be run locally. 
+To run tests locally, you'll need `npm`, which is a standard part of any [node.js installation](https://nodejs.org/en/download/).
+Alternatively, you can also use [`yarn`](https://yarnpkg.com/) instead of `npm`.
+In this case replace all occurrences of `npm` with `yarn` below.
+
+First you'll need to install everything with npm once. Just navigate to the root of this repository and on 
+your command line run:
+
+```bash
+npm install
+```
+
+Then to check markdown formatting and test the examples against the JSON schema, you can run:
+
+```bash
+npm run test
+```
+
+This will spit out the same texts that you see online, and you can then go and fix your markdown or examples.
+
+To just check the markdown run:
+
+```bash
+npm run check-markdown
+```
+
+To just check the examples run:
+
+```bash
+npm run check-examples
+```
+
+If the tests reveal formatting problems with the examples, you can fix them with:
+
+```bash
+npm run format-examples
+```